1. Field of the Invention
The present invention relates to a cryogenic compressor for use in machines designed to generate cryogenic temperatures, for examples, stirling cryogenic apparatuses
2. Description of the Relates Art
Machines which are adapted for generating cryogenic temperatures, i.e., stirling cryogenic apparatuses, employ a cryogenic compressor having a reciprocating piston as one of the principal constituent elements. This compressor is generally designed to compress a gas such as helium gas. This sort of conventional crank type compressor will be described hereinunder with reference to FIGS. 4 to 6.
Referring to FIGS. 4 and 5, the reference numeral 1 denotes an electric motor which drives a crankshaft 2. A connecting rod 3 has its large end portion fitted and thereby supported on an eccentric portion of the crankshaft 2 through a bearing 4. A piston 5 is connected to the small end portion of the connecting rod 3 so that the piston 5 is reciprocatable within a cylinder 6. A piston ring 7 is fitted on the piston 5 so as to seal the clearance space between the piston 5 and the cylinder 6. A bearing 8 is provided so as to bear the crankshaft 2 on a motor casing 9. A crank case 10 is provided between the cylinder 6 and the casing 9, and a gas pipe 11 is connected to the top of the cylinder 6. The reference numeral 12 denotes a compression space which is defined within the cylinder 6, while the numeral 13 denotes a buffer space defined within the crank case 10, and these spaces 12 and 13 are partitioned off from each other by the piston 5 and the piston ring 7.
In the cryogenic compressor arranged as described above, as the motor 1 is activated, the crankshaft 2 is rotated, and the piston 5 is reciprocated within the cylinder 6 through the connecting rod 3, thereby repeating compression and expansion of the compression space 12, and thus effecting discharge and suction of working gas through the gas pipe 11. In response to this operation, the gas pressure P.sub.C within the compression space 12 changes toward both high- and low-pressure sides with respect to the gas pressure P.sub.B within the buffer space 13 in accordance with the crank angle as shown in FIG. 6, and in accordance with the change in the gas pressure P.sub.C, the bearing load, connecting rod load and piston lateral pressure also change toward both high- and low-pressure sides as shown in FIG. 6. In this figure, the crank angle is set in such a manner that the angle which is made when the piston is at the top dead center is 0.degree..
The conventional cryogenic compressor is arranged as detailed above, and the gas pressures within the compression and buffer spaces change as shown in FIG. 6, thus causing the working gas to be breathed in and out between the compression and buffer spaces. This breathing action involves the problem that the gas in the buffer space, which is contaminated by contaminative particles such as those which are generated from wearing caused by the slide contact between the piston ring and the cylinder and which drop gravitationally to float within the buffer space, may enter the compression space to contaminate the working gas, resulting in the function of the cooling cycle being damaged. Further, since the direction of change of each of the bearing load, connecting rod load and piston lateral pressure changes in accordance with the crank angle, an impulsive sound may be generated due to clearance spaces which are present at the bearings, connecting rod and piston unit. In addition, the impact accelerates the wear of each of the above-described parts, resulting in the life of the compressor being shortened.